1. Field of the Invention
This invention relates generally to chair controls for tiltable chairs and more particularly, to a safety feature for use with chair controls on tiltable chairs.
2. Description of the Prior Art
Tiltable chairs of the prior art generally consist of a back portion, a seat portion, a chair control and a base portion. The chair control pivotally connects the base portion of the chair to the seat portion and allows the tilting of a part of the chair in a rearwards and backwards direction when rearward pressure is applied to the back portion of the chair by the user thereof. The chair control is adapted to return the tilting portion of the chair to a resting position when this pressure is released.
These chair controls consist essentially of a fixed frame portion secured to the base portion of the chair, a moveable frame portion secured to the tilting portion of the chair (either the seat or the back of the chair) and a biasing means which pivotally connects the fixed frame portion to the moveable frame portion thereby allowing the seat or the back of the chair to be tilted.
The biasing means usually comprises an elongated bolt which extends from the interior of the fixed frame portion through the moveable frame portion and marginally beyond. The head of the bolt is placed in the fixed frame portion and a slot or groove is provided in the vertical wall of the fixed frame portion in which the head of the bolt may pivot. The shaft of the bolt extends through the fixed frame portion, through the length of the moveable frame portion and marginally beyond.
A helical spring is inserted on that portion of the bolt within the moveable frame portion and the interior end of this spring contacts with the interior vertical wall of the moveable frame portion. A tension control means is inserted on the free end of the bolt. This tension control means usually comprises a pressure plate in contact with the spring, a short sheath about the bolt and affixed to the pressure plate and extending outwards to a handwheel. The interior of the sheath is screw-threaded corresponding to the screw-threading on the end of the bolt.
In order to create tension in the spring, the handwheel is tightened thereby causing the pressure plate to move inwards contracting the helical spring. Thus, by moving the position of the handwheel, the amount of tension in the spring may be increased or reduced.
When the user of the chair applies rearward pressure to the back portion of the chair, the bolt pivots on its head in the corresponding slot in the fixed frame portion and the moveable frame portion moves upward thereby causing the seat and back portions of the chair to tilt rearwards. The tension in the helical spring will cause the device to pivot back on the head of the bolt and thus return the tilted portion of the chair to the resting position once the user of the chair releases the rearward pressure.
However, a serious safety problem occurs if the bolt of the biasing means should break. If the bolt should break at any point between the head of the bolt and the handwheel, the peripheral end of the bolt and the tension control means will project forward possibly causing severe damage to the user of the chair or any piece of furniture situated in front of the chair. Realizing that the helical spring of the biasing means is under constant tension and the amount of frictional wear on the head of the bolt, it has been found that many of the bolts will break after a period of use of the chair. This presents a serious danger to the user of the chair as the user's legs are normally directly in front of the tension control means and certainly in its path should it project forward. Also, if the operator of the chair is not directly in front of the tension control means, there is usually a piece of furniture in front of the chair and the tension control means would severely damage this furniture in this forward path.